1. Field of the Invention
The invention relates in general to a novel phosphor having high brightness and durability, a method for making the phosphor, a phosphor manufactured using the method, and particularly a red phosphor emitting light with wavelength of red light when excited and the applications related to devices such as displays or light-emitting diodes. The invention also provides a light emitting device comprising the red phosphor.
2. Description of the Related Art
By the demands of energy conservation and environmental protection, developing illumination light sources being highly efficient and energy saving and conforming to the environmental protection needs has become an important research topic. In particular, white light-emitting diodes (LED) have further become an important technology to replace the traditional illumination lamps, because they have the advantages of small volumes, low heat generation, low electricity consumption, long lifetime, and etc., and do not have the drawbacks of high electricity consumption and fragility of incandescent lamps and mercury contamination of wastes from fluorescent lamps. At present, the white light-emitting devices used for illumination are mostly using blue light as the exciting light source to collocate with yellow phosphors as the main trend. However, the white light emitted from the above-mentioned white light-emitting device is less sufficient in the red light wavelength region, such that the color rendering property and color saturation of the white light is evidently insufficient. In addition, the conventional yellow phosphor has poor illumination efficiency which makes white light having poor brightness. In order to solve the above-mentioned problems, in recent years, there have been constructive developments to mix phosphors capable of emitting red light into yellow phosphors to improve the color rendering property and color saturation of white light, and the red phosphor can be utilized to compensate the drawback of low illumination efficiency of yellow phosphor.
The known red phosphor for now, such as Sr2Si5N8:Eu, CaAlSiN3:Eu or sialon phosphor (represented by a general formula MzSi12-(m+n)Alm+nOnN16-n). However, due to the low heat tolerance of the crystal of the phosphor Sr2Si5N8:Eu, it suffers from the drawback of the decrease of brightness and the color rendering property after a long-term use. Although sialon phosphor does not have problems related to durability, of which the luminous brightness is evidently insufficient, therefore, it is not popularly used for commercial applications. Although phosphor CaAlSiN3:Eu has a nice durability and a nice brightness compared to sialon phosphor, the industry is still looking forward to phosphors with higher brightness, making light emitting devices having higher illumination efficiency than those of the known phosphor.
The luminous brightness, of the red phosphors of CaAlSiN3:Eu such as CamAlaSibNn:Euz in which (m+z):a:b:n=1:1:1:3, can be increased by the addition of alkali metals. However, the improvement range for the actual brightness is not large. In addition, the retention rate of the brightness of phosphors is evidently decreased. Therefore, the effect of the improvement is poor, and the optimization effect is not realized, such that the actually industry needs can not be satisfied.
Besides, the composition of red phosphors of CaAlSiN3:Eu has been adjusted, for example, Al/Si is adjusted to be larger than 1. Although the luminous brightness of phosphors can be increased, the retention rate of the brightness shows a trend of obvious decrease. Therefore, the luminous brightness is difficult to be substantially increased.
According to the above discussion, there is still a need for developing a red phosphor which has higher brightness and higher durability compared to the red phosphors of the current technology, and of which the practicability and the color rendering property of the white light can be increased in the sequent applications.